Cross-Border renewable energy supplies must be developed urgently to protect future electricity services, Northern Ireland Secretary of State Peter Hain has warned.
During a visit to Dublin, Mr Hain said the Republic and Northern Ireland "are both at the end of a very long supply chain starting in Russia".
He is to launch a £60 million investment programme in renewable energy next month to make the North "a world-class centre" for green energy.
"We have got to look at our energy needs. We both face common problems of supply. We need to develop tidal, offshore wind supplies.
"We have got to make sure that the lights do not go out in the future, North or South. That is the big challenge.
"The electricity and gas inter-connectors offers the island some security of supply from the UK, but the UK's own gas reserves are falling," he said.
The Republic and Northern Ireland will shortly begin to co-operate in the international battle for foreign direct investment. "I do, of course, accept that often in chasing investment the Northern and Southern economies may be in competition with each other.
"It should be possible to identify areas in which we can co-operate and then play to our respective strengths.
"This can be a win-win situation. Northern Ireland can help in situations where there are skill shortages in the Republic, for instance, rather than seeing the whole project disappear off to eastern Europe.
"Very often the real competition is not between North and South, but between the island of Ireland and places like eastern Europe," he went on.
Speaking to the Dublin Chamber of Commerce last night, Mr Hain said the Republic and Northern Ireland "have nothing to lose, and everything to gain.
"This is, in a very real sense, a case when it is possible for Northern Ireland to have the best of both worlds, benefiting by being part of a strong UK economy by maximising the trading opportunities within the island of Ireland.
"In saying that, I am not making any kind of political or constitutional point. It is just common sense," he told a chamber dinner.
Mr Hain said he has agreed with Minister for Foreign Affairs Dermot Ahern to carry out "an economic audit.
"I expect that that will demonstrate other areas in which the historic lack of effective co-operation has hindered both economies and where there is scope to make more progress," he said.
He acknowledged that unionist politicians had bridled in the past when he had raised the prospect of greater economic co-operation. "Once everyone understood what I was saying there has been a recognition of the fact that it is common sense.
"There is an increasing recognition amongst unionists that we sink, or swim together. We are a small island in a world where India and China are gobbling up jobs and exports," he said.
The recent agreement for cross-Border cancer services will improve patients' lives, he added.
"It makes a great deal of sense and I hope that we will see the first Donegal patient receiving treatment in Belfast by the late summer," he told the chamber.